Generally, methods of obtaining 1,3-butadiene, the demand for which is gradually increasing in petrochemical markets, include naphtha cracking, direct dehydrogenation of n-butene, and oxidative dehydrogenation of n-butene. However, the naphtha cracking process, which is responsible for 90% of the 1,3-butadiene that is supplied, entails high energy consumption due to high reaction temperatures. As well, because this process is not a single process for producing only 1,3-butadiene, investment in and management of a naphtha cracker are difficult to optimize in order to meet the production demand of 1,3-butadiene. That is, to meet the increased butadiene demand through the above process, more novel naphtha crackers need to be established, and accordingly, raffinate components other than 1,3-butadiene are produced in surplus. In addition, the direct dehydrogenation of n-butene, which is an endothermic reaction, requires high-temperature and low-pressure conditions to produce 1,3-butadiene at high yield, and is thermodynamically disadvantageous, and is thus unsuitable for commercially producing 1,3-butadiene [M. A. Chaar, D. Patel, H. H. Kung, J. Catal., vol. 109, pp. 463 (1988)/E. A. Mamedov, V. C. Corberan, Appl. Cata. A, vol. 127, pp. 1 (1995)/L. M. Madeira, M. F. Portela, Catal. Rev., vol. 44, pp. 247 (2002)].
In addition, the oxidative dehydrogenation of n-butene is a reaction between n-butene and oxygen that produces 1,3-butadiene and water. This reaction is thermodynamically advantageous because water, which is stable, is produced as a product, and is also commercially advantageous because 1,3-butadiene may be obtained at high yield even at decreased reaction temperatures, without the need to additionally apply heat, thanks to exothermic properties. Further, this process additionally produces steam and is thus advantageous in terms of energy reduction. Hence, the oxidative dehydrogenation of n-butene for the production of 1,3-butadiene is considered to be an effective alternative that enables the production of 1,3-butadiene through a single process. In particular, when a C4 raffinate-3 or C4 mixture including impurities, such as n-butane, is directly used as a source of n-butene without an additional separation process, an advantage of adding high value to surplus C4 raffinate components may be realized. Specifically, the C4 raffinate-3 mixture, which is the reactant used in the present invention, is an inexpensive C4 raffinate remaining after the separation of useful compounds from a C4 mixture produced through naphtha cracking. More specifically, a first mixture remaining after extracting 1,3-butadiene from a C4 mixture produced through naphtha cracking is called raffinate-1, a second mixture remaining after extracting isobutylene from the raffinate-1 is called raffinate-2, and a third mixture remaining after extracting 1-butene from the raffinate-2 is called raffinate-3. Therefore, the C4 raffinate-3 or C4 mixture is composed mainly of 2-butene (trans-2-butene and cis-2-butene), n-butane, and 1-butene.
As mentioned above, according to the oxidative dehydrogenation of n-butene (1, butane, trans-2-butene, cis-2-butene), n-butene reacts with oxygen, thus producing 1,3-butadiene and water. Although the oxidative dehydrogenation of n-butene is an effective alternative that produces 1,3-butadiene through a single process, this reaction is supposed to cause many side-reactions, including complete oxidation, etc., due to the use of oxygen as the reactant. Thus, the development of catalysts that maximally inhibit such side-reactions and have high selectivity for 1,3-butadiene is of utmost importance. The catalysts for use in the oxidative dehydrogenation of n-butene, known to date, include ferrite-based catalysts [R. J. Rennard, W. L. Kehl, J. Catal., vol. 21, pp. 282 (1971)/W. R. Cares, J. W. Hightower, J. Catal., vol. 23, pp. 193 (1971)/M. A. Gibson, J. W. Hightower, J. Catal., vol. 41, pp. 420 (1976)/H. H. Kung, M. C. Kung, Adv. Catal., vol. 33, pp. 159 (1985)/J. A. Toledo, M. A. Valenzuela, H. Armendariz, G. Aguilar-Rios, B. Zapzta, A. Montoya, N. Nava, P. Salas, I. Schifter, Catal. Lett., vol. 30, pp. 279 (1995)], tin-based catalysts [Y. M. Bakshi, R. N. Gur'yanova, A. N. Mal'yan, A. I. Gel'bshtein, Petroleum Chemistry U.S.S.R., vol. 7, pp. 177 (1967)], bismuth molybdate-based catalysts [A. C. A. M. Bleijenberg, B. C. Lippens, G. C. A. Schuit, J. Catal., vol. 4, pp. 581 (1965)/Ph. A. Batist, B. C. Lippens, G. C. A. Schuit, J. Catal., vol. 5, pp. 55 (1966)/M. W. J. Wolfs, Ph. A. Batist, J. Catal., vol. 32, pp. 25 (1974)/W. J. Linn, A. W. Sleight, J. Catal., vol. 41, pp. 134 (1976)/W. Ueda, K. Asakawa, C.-L. Chen, Y. Moro-oka, T. Ikawa, J. Catal., vol. 101, pp. 360 (1986)/Y. Moro-oka, W. Ueda, Adv. Catal., vol. 40, pp. 233 (1994)/R. K. Grasselli, Handbook of Heterogeneous Catalysis, vol. 5, pp. 2302 (1997)].
Among these catalysts, the bismuth molybdate-based catalyst includes bismuth molybdate catalysts composed exclusively of bismuth and molybdenum oxide and multicomponent bismuth molybdate catalysts further comprising various metal components. Pure bismuth molybdate is present in various phases, and, in particular, three phases including α-bismuth molybdate (Bi2Mo3O12),β-bismuth molybdate (Bi2Mo2O9) and γ-bismuth molybdate (Bi2MoO6) are known to be useful as catalysts [B. Grzybowska, J. Haber, J. Komorek, J. Catal., vol. 25, pp. 25 (1972)/A. P. V. Soares, L. K. Kimitrov, M. C. A. Oliveira, L. Hilaire, M. F. Portela, R. K. Grasselli, Appl. Catal. A, vol. 253, pp. 191 (2003)]. However, a process of preparing 1,3-butadiene through oxidative dehydrogenation of n-butene in the presence of a pure bismuth molybdate catalyst having a single phase is unsuitable for commercialization, attributable to the production of 1,3-butadiene at low yield [Y. Moro-oka, W. Ueda, Adv. Catal., vol. 40, pp. 233 (1994)]. As an alternative thereto, in order to increase activity for the oxidative dehydrogenation of n-butene, attempts to prepare multicomponent bismuth molybdate catalysts comprising not only bismuth and molybdate but also various metal components have been made [M. W. J. Wolfs, Ph. A. Batist, J. Catal., vol. 32, pp. 25 (1974)/S. Takenaka, A. Iwamoto, U.S. Pat. No. 3,764,632 (1973)].
Some patents and literature have reported multicomponent bismuth molybdate catalysts for the oxidative dehydrogenation of n-butene. Specifically, many reports have been made of the oxidative dehydrogenation of 1-butene at 520° C. using a mixed oxide catalyst composed of nickel, cesium, bismuth, and molybdenum, resulting in 1,3-butadiene at a yield of 69% [M. W. J. Wolfs, Ph. A. Batist, J. Catal., vol. 32, pp. 25 (1974)], of the oxidative dehydrogenation of a C4-mixture including n-butane and n-butene at 470° C. using a mixed oxide catalyst composed of cobalt, iron, bismuth, magnesium, potassium, and molybdenum, resulting in 1,3-butadiene at a maximum yield of 62% [S. Takenaka, H. Shimizu, A. Iwamoto, Y. Kuroda, U.S. Pat. No. 3,998,867 (1976)], and of the oxidative dehydrogenation of 1-butene at 320° C. using a mixed oxide catalyst composed of nickel, cobalt, iron, bismuth, phosphorus, potassium, and molybdenum, resulting in 1,3-butadiene at a maximum yield of 96% [S. Takenaka, A. Iwamoto, U.S. Pat. No. 3,764,632 (1973)].
In this way, when the multicomponent bismuth molybdate catalyst disclosed in the above literature is used, 1,3-butadiene may be obtained at a very high yield, but limitations are imposed on increasing the catalytic activity because the catalyst can be prepared only through the addition of simple metal components and changes in the ratio thereof. Further, the catalytic activity is drastically decreased over the reaction time, and thus, to increase the catalytic activity, additional metal components must be continuously added, and thus the catalyst has a very complicated composition and it is difficult to ensure reproducibility. In the above conventional techniques, only pure n-butene (1-butene or 2-butene) is used as the reactant, or otherwise, even if a mixture of n-butane and n-butene serves as the reactant, a C4 mixture including n-butane in a small amount less than 10 wt % is used. Accordingly, in the case where the amount of n-butane is increased, the yield of 1,3-butadiene is expected to decrease. In order to use a C4 mixture including a large amount of n-butene as the reactant in an actual petrochemical process, a process of separating n-butene from the other C4 mixture components should be essentially performed, remarkably decreasing economic efficiency. As a typical example, in a commercial process using a ferrite catalyst, a C4 mixture in which the amount of n-butane is maintained as low as less than 5 wt % is used as the reactant.
As mentioned above, the literature and patents regarding the catalyst and process for preparing 1,3-butadiene through the oxidative dehydrogenation of n-butene are characterized in that pure 1-butene, 2-butene or a mixture thereof is used as the reactant, or otherwise, a C4 mixture including a very large amount of n-butene is used as the reactant, and further, multicomponent metal oxide having a very complicated composition, resulting from the addition of simple metal components and changes in the ratio thereof, is used as the catalyst. However, cases in which 1,3-butadiene is prepared from a C4 raffinate, including C4 raffinate-3 or a C4 mixture having a high concentration of n-butane, in the presence of a multicomponent bismuth molybdate catalyst comprising relatively simple metal components prepared through coprecipitation using a coprecipitation solution, the pH of which is adjusted, have not yet been reported.